Disclosed herein are hot melt or phase change inks and methods for the use thereof. More specifically, disclosed herein are hot melt or phase change inks particularly suitable for use in phase change ink jet printing processes with reduced energy requirements. One embodiment is directed to a phase change ink composition comprising an ink carrier and a colorant, said ink being suitable for use in an indirect printing process wherein the ink is jetted from a printhead onto a heated intermediate transfer member and subsequently transferred from the intermediate transfer member to a final recording substrate, wherein: (a) the ink can be jetted from the printhead onto the intermediate transfer member when the ink is maintained at a temperature of about 125° C. or lower; (b) the ink can be jetted without purging from a printer maintained at a standby temperature of about 100° C. or lower; and (c) the ink has a cohesive failure temperature of at least about 56° C.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labelling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 3,653,932, U.S. Pat. No. 4,390,369, U.S. Pat. No. 4,484,948, U.S. Pat. No. 4,684,956, U.S. Pat. No. 4,851,045, U.S. Pat. No. 4,889,560, U.S. Pat. No. 5,006,170, U.S. Pat. No. 5,151,120, U.S. Pat. No. 5,372,852, U.S. Pat. No. 5,496,879, European Patent Publication 0187352, European Patent Publication 0206286, German Patent Publication DE 4205636AL, German Patent Publication DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
U.S. Pat. No. 6,860,930 (Wu et al.), the disclosure of which is totally incorporated herein by reference, discloses a phase change ink composition comprising (a) a colorant and (b) a carrier comprising a polyamide, wherein the polyamide component of the carrier contains at least about 10 percent by weight of a branched triamide.
U.S. Patent Publication 2005/0130054 (Yuan et al.), the disclosure of which is totally incorporated herein by reference, discloses wax based inks for phase change/hot melt inkjet printing or thermal transfer printing applications. Also disclosed are waxes useful for toners for use in electrostatographic printing applications. Both materials are prepared using a wax having a narrow melting range. The narrow melting range of the wax reduces energy requirements in printing applications. The use of the waxes also promotes release for high speed printing and especially promotes fast drying in wax based ink applications.
U.S. Pat. No. 6,001,904 (Matzinger et al.), the disclosure of which is totally incorporated herein by reference, discloses phase change (hot melt) ink compositions for use in a phase change (hot melt) ink jet recording device in which recording is conducted by thermally melting the ink at a temperature above ambient temperature (20° C.) to provide prints that possess high quality images, scratch resistance, abrasion resistance, low-temperature storage stability and flexibility, offset and pick resistance, adhesion, and other desired properties to comprise: (a) from about 0.1% to about 30% of one or more colorants; and (b) from about 0.1 to about 99.9% of one or more reversibly-crosslinked-polymers. Components other than those listed above may be included in the ink compositions to achieve specific printer, substrate, or end use requirements. Furthermore, the invention also includes methods for the preparation of reversibly-crosslinked-polymers and for their use in the above-described inks.
U.S. Pat. No. 6,923,853 (Kremers et al.), the disclosure of which is totally incorporated herein by reference, discloses a meltable ink which is solid at room temperature, which ink is suitable for use in an indirect printing process, in which printing process the ink is transferred, by the use of an inkjet printhead, to a transfer element, whereafter the ink is transferred to a receiving material under pressure from the transfer element, the ink having a composition such that it is pressure-transferable at a temperature between a bottom temperature limit and a top temperature limit, wherein the ink has a deformation energy of less than 20×105 Pa·s at a temperature equal to said top temperature limit.
While known compositions and processes are suitable for their intended purposes, a need remains for improved phase change ink compositions. In addition, a need remains for phase change inks that can be jetted at temperatures below about 125° C. Further, a need remains for phase change inks that can be jetted with reduced energy requirements. Additionally, a need remains for phase change inks that can be jetted with less expensive printheads. There is also a need for phase change inks that enable improved thermal stability of the inks manifested as the color's stability over time when heated in printers. In addition, there is a need for phase change inks that enable improved printer reliability. Further, there is a need for phase change inks that enable quick recovery times from standby mode. Additionally, there is a need for phase change inks that enable printing with “instant-on” mode. A need also remains for phase change inks that exhibit desirable viscosity values at reduced printing temperatures. In addition, a need remains for phase change inks that enable the aforementioned advantages and also exhibit good printing characteristics, such as transfixing properties (including dither and solid fill dropout performance), acceptable jetting reliability, folding and creasing performance, color intensity, recovery after standby mode, and the like. Further, a need remains for phase change inks that generate images with improved hardness. Additionally, a need remains for phase change inks that generate images with improved gloss. There is also a need for phase change inks that exhibit reduced sweating; sweating is a problem wherein some ink ingredients migrate to the surface of solid ink sticks and aggregate at the ink stick surface inside the printer; the sticky “sweat” gradually drains down to the bottom and can cause the ink sticks to be difficult to slide in the ink load racks in the printers. In addition, there is a need for phase change inks that generate images with reduced showthrough when printed on paper substrates. Further, there is a need for phase change inks that exhibit reduced clogging of printheads while exhibiting all of the aforementioned advantages. Additionally, there is a need for phase change inks that enable reduced standby temperatures of phase change ink jet printheads without leading to clogging of the printhead or the need for a purge upon recovery to the operational jetting temperature. A need also remains for phase change inks with desirably low freezing points. In addition, a need remains for phase change inks that transfer efficiently from an intermediate transfer member to a final recording substrate when the intermediate transfer member is at a desirably high temperature to enable efficient transfer member cooling, which allows for efficient heat transfer and avoids automatic printer shutoff or slowdown from overheating of the intermediate transfer member by the ink, while also enabling jetting of the ink at a desirably low temperature. Further, a need remains for phase change inks that exhibit desirably high smudge temperatures when still-hot prints pass along guidance tracks in the printer, thereby reducing accumulation of ink along these guidance tracks that could later be transferred to blank paper.